On the role of defects in decreasing the extra 3.3/3.95 and 4.5 V redox steps in Li–Mn–O spinels

LiMn2O4 spinels were studied with the aim of assessing the role of different types and amounts of defects in blocking the phase transition from spinel to double hexagonal that is associated with anomalous 4.5 and 3.3/3.95 V redox steps. The influence of the type of MnO2 precursor (β or γ, both with diverse amounts of stacking faults), the effect of introducing defects in the final spinel by ball milling or of cationic subsitutions on the spinel 16d sites (Al or Li) were examined. Electrochemical experiments performed on all these defective samples indicate that defects block the phase transition to a certain extent. The introduction of either Li or Al in spinel 16d sites proved to be the most effective to prevent the structural transformation, and thus eliminate the anomalous redox steps that are detrimental to the electrochemical performances of LiMn2O4.